My favorite pokemon are Cradily and Mantine. They are both UU but can also be very powerful in OU. With cradily's stockpile the defense can handle a lot, and you can recover when hp gets low. If you are really daring you can do what i do and do a swordsdance for attack. Mine has swept more than half a team many times. Mantine is a great special wall, but electric seems to be a problem, so it is best to have a pokemon resistant to electric in your party.